Security alarm systems are becoming increasingly popular in residential communities. The most common form of sensor in residential areas and homes is the form of fire and smoke detector. However, there has been increased use in residential areas of intrusion or burglar alarms and also devices which monitor the status of various appliances in the home, whether it be a gas-fired water heater, gas-fired furnace, freezers and the like. Similar alarm systems are, of course, used in industry. As the systems are expanded at each installation, it becomes more and more important to have a central monitoring device which determines the status of all of the sensors to ensure that they are operative at all times and which is to be located in an area such that, when an alarm is sounded, the type of alarm and its whereabouts can be determined.
This has resulted in the demand for a central monitor which can communicate with all forms of sensors in a home or industrial installation. To accomplish this objective, transmitters have been devised for coupling with the various sensors and transmitting information to a receiver of a central monitor system. The information transmitted may identify the type of alarm and its location. In industrial applications, radio transmitters are not frequently used, because it is easy to install wiring to hook up the various sensors directly with the central monitor system. However in the home, wiring is unattractive and with the use of radio receivers and transmitters, the wiring is eliminated.
In residential applications, it is important to distinguish the security alarm system of one household relative to all adjacent households. This prevents a transmitter in one household transmitting an alarm condition and having it picked up by the neighbouring household alarm system. To avoid this, each transmitter is coded with information, which not only identifies the particular alarm system, but also the sensor which is transmitting the alarm. This requires that some form of memory be provided with each transmitter and with the receiver. Presently this has been accomplished by use of a memory which is precoded before the unit is sold, offering little flexibility to the householder or by use of memories which may be coded by mechanically flipping switches. By using a predetermined format, the code for the system can be entered into the device by flipping the appropriate switches along with a code for the particular sensor being coupled with a transmitter. Such preprogramed or limited mechanical switching program memories offer little flexibility and to the average consumer are difficult to program. Since the program is provided by way of switches, they can be accidentally altered or could be intentionally altered by an intruder into a household. In addition, the transmitters normally have their own power supply which is separate from the sensor. It usually involves locating the transmitter outside of the sensor, adding to the bulkiness of the overall system and detracting from the attractiveness of the various sensors which are visible, such as the smoke and perhaps the intrusion detectors.
The improvements in security systems, according to this invention, overcome the above problems in providing a far more flexible system to accommodate variations of each household and which can be readily installed by the consumer.